This invention relates to a clutch drum.
FIG. 1 shows a conventional frictional clutch for use in an automatic transmission. A press-formed clutch drum 1 has a spline portion 1a. A snap ring groove 1b is formed in each extruded angles of the spline portion 1a. A snap ring 2 is set in the snap ring grooves 1b so that plural clutch plates 3 can be prevented from moving in an axial direction as well-known.
FIGS. 2 through 4 show in detail such snap ring grooves in a conventional clutch drum. A snap ring groove 13 is formed in each extruded angle or inward protruding portion 12 in a clutch drum 11.
The snap ring grooves 13 are formed by the following steps: Two parallel cutting lines are formed in a predetermined portion of each extruded angle 12 where the snap ring groove 13 is to be formed. The distance between the two cutting lines is slightly longer than the width of the snap ring 14. The portion of the extruded angles 12 between the cutting lines is pressed out so as to form the grooves 13. The reference 15 designates such pressed-out portions. A recess resulting from the pressing-out constitutes the snap ring groove 13.
In the above-mentioned conventional clutch drum, however, the pressed-out portions 15 are partly cut off from the body of the clutch drum 11 along the cutting lines so as to be weak.
For such a reason, a thick steel plate must be used in order to avoid the rupture of the pressed-out portions 15 defining the snap ring grooves 13. In addition, a large size of special machine for carrying out the steps of forming two cutting lines and pressing out the clutch drum must be used. Also, for the same reason, it takes a long production time.